Magnet wire is insulated by passing a bare conductor through a bath of a liquid enamel, up through a die that removes excess enamel, then through an oven where the enamel is cured. Ideally, the conductor is in the exact center of the insulation, so that the thickness of insulation is uniform completely around the wire. However, for various reasons, the center of the insulation may not coincide with the center of the conductor, so that one side of the wire is inadequately insulated while the opposite side has more insulation than is needed. If the eccentricity of the insulation is too great, the wire must be rejected and scrapped.
The eccentricity of the insulation is usually determined by cutting a sample from each end of the spool of wire. Cross-sections taken from the two samples are prepared and are examined under the microscope to visually determine the eccentricity of the insulation. While this method is accurate, it is very time consuming, and can take from 15 minutes to several hours to complete. Also, only a single cross-section of each sample is examined, which may not be representative of the entire sample or the spool. As a result, if the insulation on the particular cross-section examined is more eccentric than the rest of the spool, the entire coil of wire may be mistakenly scrapped, and if the insulation on the particular cross-section examined is less eccentric than the rest of the spool, the coil of wire may be mistakenly accepted.